Congestive heart failure (CHF) is a disease condition that involves the loss of pumping ability by the heart. Often CHF is accompanied by fluid accumulation in the body tissues, and especially in the lungs. CHF usually develops slowly, such that symptoms may not appear until the condition has progressed over time. This is because the heart deals with and essentially hides the underlying problems by making adjustments that delay—but do not prevent—the eventual loss in pumping capacity. For example, the heart may cope with and hide the effects of CHF by enlarging (i.e., dilatation) to allow more blood to enter into the heart. The muscle fibers of the heart may also thicken (i.e., hypertrophy) to strengthen the heart muscle and thereby contract more forcefully and pump more blood. The heart may also beat more often to increase circulation. By making these adjustments, or compensating, the heart can temporarily make up for losses in pumping ability, sometimes for years. However, compensation has its limits. Eventually, the heart cannot offset the lost ability to pump blood, and the signs of CHF will appear.
Traditionally, a patient afflicted with CHF would receive drug therapy and make healthy lifestyle changes. Recently, there has been a movement towards further treating certain CHF patients with pacing therapy. Here, it has been found that the contractions of the left ventricle and the right ventricle may become unsynchronized, for example, as a result of a bundle branch block. This loss of synchronization between the left and right ventricles can significantly reduce the heart's pumping ability. Implantable pacing devices can be configured to apply therapy (e.g., bi-ventricular pacing) to selected areas of the heart to improve the heart's pumping ability. However, before shock therapy can be applied, there is a need to determine the applicable pacing parameters for the patient.
U.S. Pat. No. 6,280,389, issued to Ding et al., titled “Patient Identification for the Pacing Therapy Using RV-LV Pressure Loop,” teaches that not all CHF patients may benefit from pacing therapy. Here, for example, Ding et al. provide methods for determining if a CHF patient may benefit from pacing therapy based on measured pressure levels within the left ventricle (LV) and right ventricle (RV). The measured pressure level data can be plotted to form a loop. Based on this RV-LV pressure loop, it can be determined whether a CHF patient should receive pacing therapy.
Another useful data set is a ventricle's pressure and volume, which also forms a loop during a cardiac cycle. The resulting pressure-volume (P-V) loop can be used to diagnose and treat deceases, such as CHF.
Measuring the pressure within the RV and/or LV can be accomplished during acute treatment, for example, within a hospital setting wherein catheters having leads with pressure sensors may be placed within each ventricular chamber. However, such sensors may not be suited for chronic diagnostics and treatment using an implantable device. There is significant trepidation in placing leads within the LV during chronic treatment, since the blood pressure within this chamber is much higher compared to the RV. There is a danger, should a lead break within the LV, that the broken piece(s) may flow with the blood to the patient's brain and cause a stroke.
Consequently, there is a need for methods and apparatuses that can generate P-V-like loops (e.g., pseudo P-V loops) for the right and/or left ventricles, which can then be used to analyze/monitor a patient's cardiac condition and selectively apply/adjust stimulation-based pacing therapy. Preferably, the methods and apparatuses can be employed within implantable devices used for chronic treatment of CHF and/or other heart diseases.